1. Field of the Invention
The present invention relates to a control apparatus for a hybrid vehicle, and more specifically, the present invention relates to a control apparatus for a hybrid vehicle in which the power of an engine thereof is supplemented by power from a motor, and the power generation operation by the motor is controlled depending on electrical energy (hereinafter referred to as a state of charge) stored in an energy storage device.
Priority is claimed on Japanese Patent Application No. 2003-13526, filed Jan. 22, 2003, the content of which is incorporated herein by reference.
2. Description of Related Art
Among hybrid vehicles, a type of hybrid vehicle is known in which the state of charge of the energy storage device thereof is monitored, and when the energy storage device tends to discharge energy, the control mode of the motor thereof is changed from a discharging mode to a charging mode so that electrical energy is sent to the energy storage device from the motor, and so that the energy balance in the energy storage device is recovered (see, for example, Published Japanese Patent No. 3300294).
In the above known hybrid vehicle, a control operation is executed so that the state of charge of the energy storage device is recovered in such a manner that when the state of charge of the energy storage device decreases by a predetermined amount from the initial state of charge at the beginning of the run, an assist frequency, which is frequency of events in which the power of the engine is supplemented by the motor, is decreased, an amount of assist, which is auxiliary power to be added to the power of the engine, is decreased, and an amount of power generation during a cruise mode (i.e., an amount of charging energy for the energy storage device) is set to be greater until the state of charge of the energy storage device is recovered to a predetermined level.
By using a control apparatus for the above hybrid vehicle, when the state of charge of the energy storage device decreases by a predetermined amount, the state of charge of the energy storage device can be recovered to at least the initial state of charge; therefore, the state of charge, which is difficult to be directly measured, can be controlled so that, at least, the state of charge is not decreased; however, because the running conditions of the vehicle change every moment until the state of charge of the energy storage device is recovered to a predetermined level, it is desired that the state of charge of the energy storage device be precisely controlled depending on the running conditions of the vehicle.